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Metagonimoides oregonensis
''Metagonimoides oregonensis'' is a trematode, or fluke worm, in the family Heterophyidae. This North American parasite is found primarily in the intestines of raccoons (Procyon lotor), American minks (Neovision vision), frogs in the genus Rana, and freshwater snails in the genus Goniobasis.〔〔 It was first discovered in 1931 by E. W. Price. The parasite has a large distribution, from Oregon to North Carolina.〔 Adult flukes vary in host range and morphology dependent on the geographical location. This results in different life cycles, as well as intermediate hosts, across the United States. On the west coast, the intermediate host is freshwater snails (''Goniobasis''), while on the east coast the intermediate host is salamanders (Desmognathus). The parasites on the west coast are generally much larger than on the east coast. For example the pharynx as well as the body of the parasite are distinctly larger in Oregon than in North Carolina.〔 The reverse pattern is observed on the east coast for uterine eggs, which are larger on the west coast. In snails, there is also a higher rate of infection in female snails than in males.〔 Research on the life history traits of the parasites have been performed with hamsters and frogs as model species.
== Life Cycle ==
In order to understand the life cycle, biologists have used hamsters as model species. Hamsters are infected with adult parasites that are able to lay eggs inside their intestines.〔 While hamsters are not an ideal host, the parasite still infects the them and deposits brown eggs in the intestines. For the studies, the eggs are taken out of the hamster’s intestines and put into an incubator to resemble the intestines of the hamster giving the parasites an ideal environment to grow. It only takes 23 days of incubation for the egg to hatch into a moving, ciliated miracidium. Miracidium is the stage in which the larvae are free swimming and are able to move to its first intermediate host.〔 After continual incubation of around 4 months there was no physiological change in the miracidium, which means ''Metagonimoides oregonensis'' can start infecting its first intermediate host in less than a month. This was followed by an experiment that was testing if warm water and different solutions would created the miracidium. Testing this might answer if and when the miracidium would form and be able to infect in different geological locations. All of the trials failed leaving biologist unable to give direct answers.〔
Biologists began looking at the different life cycle stages involved in ''Metagonimoides oregonensis'' in the wild compared to the parasite in captivity. For this experiment snails were used as the intermediate host. Rediae are larvae which are produced within the sporocyst of trematodes that creates more rediae or can become cercariae.〔 Cercariae are larval trematode worms that form from rediae.〔 When the snail was infected in the wild there was no sign of immature rediae. This means there was no reproduction of the parasite. When looking at the snail in captivity though, there were signs of the immature rediae.〔 Since the snails in captivity were not being exposed to the parasite there was no reinfection occurring. In conclusion this experiment shows that rediae reproduced when they were not being continually exposed. When they were being continually exposed though, rediae were not being produced.
抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』
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